* (required) a new "btrfs" section in gnome-disk-utility/Palimpsest. When a btrfs filesystem is highlighted, the user is shown a drop-down menu that allows choosing the snapshot that will be used the next time the filesystem is mounted, and a separate text box and "create" button for creating a new snapshot immediately. (cjb)

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* (deferred) a new "btrfs" section in gnome-disk-utility/Palimpsest. When a btrfs filesystem is highlighted, the user is shown a drop-down menu that allows choosing the snapshot that will be used the next time the filesystem is mounted, and a separate text box and "create" button for creating a new snapshot immediately. (cjb)

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* (required) a yum plugin to create a timestamped snapshot just before starting each yum transaction. (josef, skvidal)

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* (finished) a yum plugin to create a timestamped snapshot just before starting each yum transaction. (josef, skvidal)

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* (optional) a patch to grub1 -- on top of the already existing patch to support btrfs in grub1 -- to allow selecting between snapshots of the boot partition.

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* (deferred) a patch to grub1 -- on top of the already existing patch to support btrfs in grub1 -- to allow selecting between snapshots of the boot partition.

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* (optional) a patch to btrfs to set an fs-specific option of which snapshot should be the next "default" to boot. This avoids having the control panel need to modify either the grub config or /etc/fstab; instead it would just set a filesystem property with btrfsctl(1).

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* (finished) a patch to btrfs to set an fs-specific option of which snapshot should be the next "default" to boot. This avoids having the control panel need to modify either the grub config or /etc/fstab; instead it would just set a filesystem property with btrfsctl(1).

== How To Test ==

== How To Test ==

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== Release Notes ==

== Release Notes ==

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To follow.

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* Users of the experimental btrfs filesystem in Fedora 13 benefit from automatic filesystem snapshots each time the yum package manager performs an installation or upgrade, and from a user interface to allow switching between snapshots.

== Comments and Discussion ==

== Comments and Discussion ==

* See [[Talk:Features/SystemRollbackWithBtrfs]]

* See [[Talk:Features/SystemRollbackWithBtrfs]]

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[[Category:FeatureAcceptedF13]]

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Btrfs is capable of creating lightweight filesystem snapshots that can be mounted (and booted into) selectively. The created snapshots are copy-on-write snapshots, so there is no file duplication overhead involved for files that do not change between snapshots.

It's important to note that these snapshots are whole-filesystem snapshots -- while we propose to create a new snapshot each time a yum transaction happens, that doesn't mean reverting to an earlier snapshot will only revert the files changed by yum! The entire root filesystem will be reverted, including users' home directories if they are on btrfs. (Because of this, a user may decide to keep /home on a separate, non-btrfs partition where it is unaffected by rollbacks they decide to initiate.)

A "rollback" to an older snapshot is not destructive to data. It switches to an earlier snapshot, and later snapshots are still available afterwards. We allow the user to choose which snapshot will be mounted next, and making that choice does not affect or destroy any other snapshots.

We are not proposing Btrfs to be the default filesystem for Fedora 13; this feature would only be present on installs where Btrfs has been optionally chosen for at least one filesystem.

Aaron is a developer whose laptop tracks Rawhide daily. There will be days where Rawhide is not bootable/usable, though. When Rawhide breaks, automated snapshots allow Aaron to easily revert to the previous day's filesystem until Rawhide's known-working again.

Barbara wishes to bisect a mysterious bug that appears to have crept in on one of her recent Rawhide updates. Performing the full-system bisection is made easier by binary searching the snapshots on her disk, to narrow down responsibility for the bug to a small list of modified packages and their versions.

Christine wishes to create weekly snapshots by hand in case she later wants to have access to older versions of the files she's been working on.

Donald has, independent of yum/rpm, somehow hosed his system and doesn't know how to recover it. He'd like to revert back to the last snapshot that was made.

Of these, the ability for our developers to feel comfortable tracking Rawhide without fear of an unusable install seems to have the most immediate utility to Fedora.

(deferred) a new "btrfs" section in gnome-disk-utility/Palimpsest. When a btrfs filesystem is highlighted, the user is shown a drop-down menu that allows choosing the snapshot that will be used the next time the filesystem is mounted, and a separate text box and "create" button for creating a new snapshot immediately. (cjb)

(finished) a yum plugin to create a timestamped snapshot just before starting each yum transaction. (josef, skvidal)

(deferred) a patch to grub1 -- on top of the already existing patch to support btrfs in grub1 -- to allow selecting between snapshots of the boot partition.

(finished) a patch to btrfs to set an fs-specific option of which snapshot should be the next "default" to boot. This avoids having the control panel need to modify either the grub config or /etc/fstab; instead it would just set a filesystem property with btrfsctl(1).

Make your root filesystem be on btrfs. This can be by selecting it in the installer, or running the btrfs migration tool from ext3 or ext4. Make sure to have a backup first!

Boot into the new btrfs system, and perform a "yum install". Does palimpsest show that a new snapshot was created? Does it allow you to set that snapshot as active for the next book without any errors?

When you reboot, verify that the application you successfully yum-installed is no longer present on the system.

Switch back to the latest "default" snapshot and reboot. Test that the yum-installed app is present once more.

Try creating a snapshot by hand using palimpsest, and set it as active for the next boot. Before rebooting, touch a file in the root directory of the filesystem. After you reboot, it should be gone.

There will be new options available if your disk contains btrfs filesystems and you run palimpsest. If there is a mounted btrfs partition, palimpsest will offer a selection of old snapshots to use at next mount, and offer the creation of new ones. If there are no btrfs mounts, the UI will be entirely unchanged.

If the grub subfeature is completed, and a user has chosen to use btrfs as their boot filesystem, users will see a list of date/timestamps corresponding to snapshots that they can select from by interrupting grub at boot-time.

All of the support needed for btrfs snapshots should be already present in the kernel. The patch to support btrfs in grub has not been committed to grub1 so far (although we note that Gentoo already carries it locally). We would have to persuade the Fedora Grub maintainer(s) to adopt the patch for the grub subfeature to be completed.

Users of the experimental btrfs filesystem in Fedora 13 benefit from automatic filesystem snapshots each time the yum package manager performs an installation or upgrade, and from a user interface to allow switching between snapshots.

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